Prior art methods and apparatus are well known for positioning a cathode ray tube (CRT) or a picture tube or a kinescope in a cabinet of a video display device for securing the CRT in a viewable position to the cabinet. In the past, the problems of accurately positioning and then securing a CRT to a cabinet were mainly associated with television receivers manufactured by the television industry. More recently, these problems have also been associated with video display terminals manufactured by the computer industry.
In both the television industry and the computer industry the essential problem of accurately positioning and then securing the CRT within the cabinet remains the same. Specifically, the CRT must first be accurately positioned within the cabinet so that the face of the CRT is flush with the bezel of the cabinet and the appropriate portion of the face of the CRT is aligned with the opening in the cabinet. Next the CRT must be permanently secured to the bezel without causing a misalignment with the face of the CRT. The connection between the CRT and the bezel must also be strong enough to withstand possible shock and vibration load as well as temperatures existing during shipping of the product and also during normal operation.
A variety of prior art mounting systems exist which have attempted to solve these problems. One common method is to attach mounting ears at each corner of the front portion of the CRT with a metal strap. The metal strap is wrapped around the mounting ears and the CRT and is then tightened and clamped. The CRT is subsequently mounted to the inner front portion of the cabinet which contains mounting holes for accepting screws. The screws are driven through holes in the mounting ears while the CRT is properly aligned with the cabinet. Once the CRT is aligned, the screws are finally tightened to provide a secure attachment of the CRT to the cabinet. A spring mounted strap is then attached to diagonally positioned ears and contacts the aquadag of the CRT to provide electrical grounding.
The above described mounting ear and screw type of system, however, has several drawbacks. This system is labor intensive due to the attachment of the ears to the CRT through the tightening and clamping of the strap to the CRT and due to the tightening down of the screws while adjusting the position of the CRT in the cabinet. In addition, this type of system requires the use of multiple fasteners which increases the cost and the complexity of the system.
In addition, securing the CRT within the cabinet in the properly aligned position is also difficult in the mounting ear and screw type of system. The tightening of the screws through the mounting ears to the cabinet, by its very nature, distorts the entire mounting apparatus during the final tightening of the screws. This tightening introduces unwanted forces to the mounting apparatus and can displace the properly aligned CRT before the CRT is finally screwed into place. When this occurs, the CRT must be loosened, repositioned, and tightened again to obtain a proper alignment.
Other hardware oriented mounting systems include the use of a rear support member which pushes the CRT into the cabinet from behind. The rear support member fits around the rear funnel portion of the CRT and includes mounting ears or other means which are then coupled to the inside front of the cabinet as previously described. In addition to the problems of multiple fasteners and of aligning the CRT to the cabinet, this type of system includes the problem of interfacing the rear support member to the rear funnel surface of the CRT, a surface which is not consistently formed to a predictable shape.
Non-hardware oriented types of mounting systems which use a bonding material to hold the CRT within the enclosure are also known. One such system mounts a CRT within a case which is shaped to essentially follow the line of the rear funnel portion of the CRT. The CRT is placed into the case, funnel end first. A space is thereby created between the funnel portion of the CRT and the case. An elastic material typically comprising silicone rubber is poured in the space between the funnel of the CRT and the inside wall of the case to hold the CRT therein. A cavity is formed between the case and the silicone rubber to provide for thermal expansion of the elastic material.
The cavity between the case and the silicone rubber restricts the axial forward shifting of CRTs mounted in these types of cases. As this system relies on mounting the rear funnel surface of the CRT to the case, it suffers from the previously mentioned problem of relying on the inaccurately formed rear funnel for mounting purposes.
Another system using a non-hardware mounting means is used in small CRTs having image areas of six inches or less and in which the anode connection is close to the front surface of the CRT. In this is system, the sides of the tube are perpendicular to the front surface of the CRT. A mounting means including a collar surrounds the sides of the CRT. A channel formed between the collar and the sides of the tube is filled with a bonding material which when hardened retains the mounting means around the CRT. The mounting means includes holes to facilitate attachment of the mounting means to a suitable support medium, such as a cabinet.
This side-mounted type of system is not suitable for larger CRT's used in video display terminals and televisions. Larger CRT's typically have tolerances of plus or minus 0.125 inch on their glass across the face dimensions. The size of this dimension makes it difficult to bond the CRT at its sides to the mounting means. Currently available structural adhesives will not cure consistently or reliably across a gap of 0.125 inches or more to form the required bond between the sides of the CRT and the collar.